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Captured CO2 converts into oxalic acid to process rare earth elements

A team lead by S. Komar Kawatra, a professor of chemical engineering at Michigan Technological University, his PhD students, Sriram Valluri and Victor Claremboux, and undergraduate Sam Root, have designed a carbon dioxide scrubber with the goal of converting the carbon dioxide that they capture into oxalic acid.

Root and Valluri are presenting their research at the Society of Mining, Metallurgy and Exploration’s annual meeting this week in Denver.

Oxalic acid is used by industry to leach rare earth elements from ore bodies. Rare earths are not presently produced in the United States; China produces 90% or more of the rare earths in the world. By producing oxalic acid domestically, it may be possible to profitably extract rare earth elements in the US, Kawatra said.

The group installed their carbon dioxide scrubber at the Michigan Tech steam plant, where they are testing with real flue gas at pilot plant scale. The steam plant produces flue gas that contains 8% carbon dioxide. The chemical engineers’ scrubber brought the emissions down to 4%; their goal is to reduce it below 2%.

In the steam plant, they tap a sample stream of flue gas from the boiler’s main exhaust line. The flue gas comes out of the burner at 300-350 degrees Fahrenheit. The sample is compressed through a filter that removes particles, then passes through a cooling unit before it enters the bottom of the scrubbing column.

A sodium carbonate solution is pumped into the top of the 11-foot-tall scrubbing column. The flue gas is bubbled up through the column. As it moves toward the top, the sodium carbonate or soda ash removes much of the carbon dioxide from the gas.

John Simmons, a Michigan Tech alumnus in the Chemical Engineering Academy at Tech and chairman of Carbontec Energy in Bismarck, North Dakota, is supporting Kawatra’s research. He says the savings to industry of this kind of carbon dioxide scrubber is enormous.

The usual method of removing carbon dioxide from emissions uses amines, nitrogen-based chemical compounds that bind the carbon dioxide. But amines cost $20,000 a ton, Simmons said. Carbonates such as the soda ash that Kawatra’s team is using cost $200 a ton.

The technology, trade-named the “Clearite VI Carbon Dioxide Capture/ Utilization Process,” was patented (Patent No. US7,919,064B2) by the inventors, S. Komar Kawatra, Tim Eisele and John Simmons, and assigned to Michigan Tech. Carbontec Energy Corporation, the technology sponsor, is the exclusive world-wide licensee and plans to commercialize the technology through joint ventures and sub-licenses.



Adding CO2 to sodium carbonate has to convert it to sodium bicarbonate via this reaction:

Na2CO3 + CO2 + H2O -> 2 NaHCO3

The stripping process has to involve converting it back.  The question is, how much energy is involved?  At least it does not require high temperatures (50°C) so low-grade heat is sufficient to drive the reaction.


Where is the monoelectronic reduction step?

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